"In some parts of Philadelphia, the urban tree canopy -- the layer of leaves, branches and stems of trees that provide shade -- is less than 5 percent.

It's not just unsightly. It's unhealthy.

It's why the Pennsylvania Horticultural Society is spearheading Plant One Million Trees, the largest multi-state, tree-planting initiative in the country. Also including New Jersey and Delaware, Plant One Million Trees aims to do just that, but first it needs Tree Tenders, or engaged and capable citizens who can recognize the need and also lead others to help restore the local tree population and reach the goal of 30 percent tree canopy.

The most recent nine-hour Tree Tenders training course, which covers tree biology, identification, stress, maintenance and pruning, just wrapped up, and we tagged along to capture the growth of the movement."